In epidemiology, prevalence is the proportion of a particular population found to be affected by a medical condition (typically a disease or a risk factor such as smoking or seat-belt use) at a specific time. It is derived by comparing the number of people found to have the condition with the total number of people studied, and is usually expressed as a fraction, a percentage, or the number of cases per 10,000 or 100,000 people.

Prevalence is the number of disease cases present in a particular population at a given time, whereas incidence is the number of new cases that develop during a specified time period.[1] Prevalence answers How many people have this disease right now? or How many people have had this disease during this time period?. Incidence answers How many people acquired the disease during [a specified time period]?. However, mathematically, prevalence is proportional to the product of the incidence and the average duration of the disease. In particular, when the prevalence is low (<10%), the relationship can be expressed as:

<m> PREVALENCE = INCIDENCE X DURATION </m> Caution must be practiced as this relationship is only applicable when the following two conditions are met: 1) prevalence is low and 2) the duration is constant (or an average can be taken)

example :

• Q)In a rural block with 1,00,000 population , 250 residents were identified with cardiovascular disease.calculate the prevalence of cardiovascular disease per 1000 population ?
• Soln = 2.5